feat: simplify bitshift logic to remove leftover overflow handling

[TomAFrench]

Description

Problem*

Resolves

Summary*

After #9373, we still have some leftover logic where we're handling the potential for bitshifts greater than the type size. This PR removes some of those cases as well as doing a few simplifications to the pow function to reduce unnecessary DOF

Additional Context

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[github-actions]

Changes to circuit sizes

Generated at commit: bcb40a8ac77a724350de238b18d8cb4e5186d01a, compared to commit: 12465f3ae45cdbd96531889e9420ad02254e17f9

🧾 Summary (10% most significant diffs)

Program	ACIR opcodes (+/-)	%	Circuit size (+/-)	%
bit_shifts_runtime	-82 ✅	-13.10%	-139 ✅	-2.76%
binary_operator_overloading	-7 ✅	-7.07%	-711 ✅	-17.70%

---

Full diff report 👇

Program	ACIR opcodes (+/-)	%	Circuit size (+/-)	%
inactive_signed_bitshift	80 (-16)	-16.67%	2,849 (-15)	-0.52%
u16_support	38 (-7)	-15.56%	2,797 (-29)	-1.03%
bit_shifts_runtime	544 (-82)	-13.10%	4,895 (-139)	-2.76%
binary_operator_overloading	92 (-7)	-7.07%	3,305 (-711)	-17.70%

[github-actions]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'Test Suite Duration'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.20.

Benchmark suite	Current: 16ad037	Previous: 12465f3	Ratio
test_report_zkpassport_noir_rsa_	1 s	0 s	+∞

This comment was automatically generated by workflow using github-action-benchmark.

CC: @TomAFrench

[github-actions]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'Compilation Time'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.20.

Benchmark suite	Current: f121f90	Previous: bae9236	Ratio
sha512-100-bytes	2.013 s	1.539 s	1.31

This comment was automatically generated by workflow using github-action-benchmark.

CC: @TomAFrench

[github-actions]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'Execution Time'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.20.

Benchmark suite	Current: 68e6bad	Previous: 29160ca	Ratio
private-kernel-inner	0.017 s	0.014 s	1.21

This comment was automatically generated by workflow using github-action-benchmark.

CC: @TomAFrench